Microstructural and associated chemical changes during the composting of a high temperature biochar: Mechanisms for nitrate, phosphate and other nutrient retention and release

Abstract

Recent studies have demonstrated the importance of the nutrient status of biochar and soils prior to its inclusion in particular agricultural systems. Pre-treatment of nutrient-reactive biochar, where nutrients are loaded into pores and onto surfaces, gives improved yield outcomes compared to untreated biochar. In this study we have used a wide selection of spectroscopic and microscopic techniques to investigate the mechanisms of nutrient retention in a high temperature wood biochar, which had negative effects on Chenopodium quinoa above ground biomass yield when applied to the system without prior nutrient loading, but positive effects when applied after composting. We have compared non-composted biochar (BC) with composted biochar (BCC) to elucidate the differences which may have led to these results. The results of our investigation provide evidence for a complex series of reactions during composting, where dissolved nutrients are first taken up into biochar pores along a concentration gradient and through capillary action, followed by surface sorption and retention processes which block biochar pores and result in deposition of a nutrient-rich organomineral (plaque) layer. The lack of such pretreatment in the BC samples would render it reactive towards nutrients in a soil-fertilizer system, making it a competitor for, rather than provider of, nutrients for plant growth.

Nutrient effect of various composting methods with and without biochar on soil fertility and maize growth

“…Beneficial effects of co-composted biochar on soil physicochemical properties and available nutrients (P-AL, K + , NO 3 − ) have previously been reported by Agegnehu et al (2016). Increased nutrient retention could be due to the formation of organic coating in co-composted biochar, which entrap or adsorb dissolved nutrients in the system Hagemann et al 2017;Joseph et al 2017).…”

“…Addition of biochar during the composting process changes the compost properties, and quality and can lead to improved physicochemical properties (organic carbon content (OC), pH, moisture content) and nutrient availability (nitrogen, phosphorous and other important nutrients) in the end product (Prost et al 2013;Zhang and Sun 2014;Agegnehu et al 2016;Vandecasteele et al 2016). The co-composting process results in an organic coating on the biochar particles which reduces the hydrophobicity of biochar and improves nutrient retention conditions leading to improved agronomic performance Hagemann et al 2017;Joseph et al 2017). This organic coating on the biochar particles also may affect soil redox (Eh) status .…”

Macadamia Nutshell Biochar for Nitrate Removal: Effect of Biochar Preparation and Process Parameters

“…The intensity of the peaks for 1000 °C are less than those for 900 °C. The peak at 3454 cm −1 indicates the presence of an − OH in a carboxylic group [36]. Peaks between 1000 and 1100 cm −1 are associated with C−O and −OH groups [37].…”

“…Both have the same peak positions, which means they have similar functional groups that allow them to adsorb similar elements [35]. The intensity of the peaks for 1000 • C are less than those for 900 • C. The peak at 3454 cm −1 indicates the presence of an − OH in a carboxylic group [36]. Peaks between 1000 and 1100 cm −1 are associated with C−O and −OH groups [37].…”

Biochar as a carrier : Trichoderma harzianum on Biochar to promote disease suppression in strawberry

“…Several sources suggested Trichoderma could be carried on biochar and could survive at higher levels for more than a few weeks (De Tender et al 2016;Debode et al 2018). It is also suggested to pre-treat biochar with either nutrients, composts or both (Hagemann et al 2017;Joseph et al 2018). It may therefore be too soon to discard biochar as carrier all together.…”